Megacolon

Megacolon
Classification and external resources
Specialty gastroenterology
ICD-10 K59.3
ICD-9-CM 564.7
DiseasesDB 32198
eMedicine med/1417
MeSH D008531

Megacolon is an abnormal dilation of the colon (also called the large intestine).[1] The dilation is often accompanied by a paralysis of the peristaltic movements of the bowel. In more extreme cases, the feces consolidate into hard masses inside the colon, called fecalomas (literally, fecal tumor), which can require surgery to be removed.

A human colon is considered abnormally enlarged if it has a diameter greater than 12 cm[2] in the cecum (it is usually less than 9 cm[3]), greater than 6.5 cm[2] in the rectosigmoid region and greater than 8 cm[2] for the ascending colon. The transverse colon is usually less than 6 cm in diameter.[3]

A megacolon can be either acute or chronic. It can also be classified according to etiology.[4]

Signs and symptoms

External signs and symptoms are constipation of very long duration, abdominal bloating, abdominal tenderness and tympany, abdominal pain, palpation of hard fecal masses and, in toxic megacolon, fever, low blood potassium, tachycardia and shock. Stercoral ulcers are sometimes observed in chronic megacolon, which may lead to perforation of the intestinal wall in approximately 3% of the cases, leading to sepsis and risk of death.

Cause

Aganglionic megacolon

Also called Hirschsprung's disease, it is a congenital disorder of the colon in which nerve cells of the myenteric plexus in its walls, also known as ganglion cells, are absent. It is a rare disorder (1:5 000), with prevalence among males being four times that of females. Hirschsprung’s disease develops in the fetus during the early stages of pregnancy. The exact genetic cause remains unsolved, although in familial cases (in which families have multiple affected patients), it seems to exhibit autosomal dominant transmission, with a gene called RET, in chromosome 10, being dominant. Seven other genes seem to be implicated, however. If untreated, the patient can develop enterocolitis.

Medication

Risperidone, an anti-psychotic medication, can result in megacolon.[5]

Toxic megacolon

Main article: Toxic megacolon

Toxic megacolon is mainly seen in ulcerative colitis and pseudomembranous colitis, two chronic inflammations of the colon (and occasionally, in the other type of inflammatory bowel disease, Crohn's disease). Its mechanism is incompletely understood. It is probably due to an excessive production of nitric oxide, at least in ulcerative colitis. The prevalence is about the same for both sexes.

In patients with HIV/AIDS, cytomegalovirus (CMV) colitis is the leading cause of toxic megacolon and emergency laparotomy. CMV may also increase the risk of toxic megacolon in non-HIV/AIDS patients with IBD.[6]

Chagas disease

Megacolon can be associated with Chagas disease.[7]

In Central and South America, the most common incidence of chronic megacolon is that observed in about 20% of patients affected with Chagas disease. Chagas is caused by Trypanosoma cruzi, a flagellate protozoan transmitted by the feces of a hematophagous insect, the assassin bug, when it feeds. Chagas can also be acquired congenitally, through blood transfusion or organ transplant, and rarely through contaminated food (for example garapa). There are several theories on how megacolon (and also megaesophagus) develops in Chagas disease. The Austrian-Brazilian physician and pathologist Fritz Köberle was the first to propose the neurogenic hypothesis based on the documented destruction of the Auerbach's plexus in the walls of the intestinal tracts of Chagas patients. In this, the destruction of the autonomic nervous system innervation of the colon leads to a loss of the normal smooth muscle tone of the wall and subsequent gradual dilation. His research proved that, by extensively quantifying the number of neurons of the autonomic nervous system in the Auerbach's plexus, that:

  1. neurons were strongly reduced all over the digestive tract;
  2. megacolon appeared only when there was a reduction of over 80% of the number of neurons
  3. these pathologies appeared as a result of the disruption of the neurally integrated control of peristalsis (muscular annular contraction) in those parts where a strong force is necessary to impel the luminal bolus of feces
  4. idiopathic megacolon and Chagas megacolon appear to have the same etiology, namely the degeneration of the myenteric plexus.

Why T. cruzi causes the destruction, however, remains to be determined. There is evidence for the presence of specific neurotoxins as well as a disorderly immune system reaction.

Diagnosis

Diagnosis is achieved mainly by plain and contrasted radiographical and ultrasound imaging. Colonic marker transit studies are useful to distinguish colonic inertia from functional outlet obstruction etiologies. In this test, the patient swallows a water-soluble bolus of radio-opaque contrast and films are obtained 1, 3 and 5 days later. Patients with colonic inertia show the marker spread throughout the large intestines, while patients with outlet obstruction exhibit slow accumulations of markers in some places. A colonoscopy can also be used to rule out mechanical obstructive causes. Anorectal manometry may help to differentiate acquired from congenital forms. Rectal biopsy is recommended to make a final diagnosis of Hirschsprung disease.

Treatment

Possible treatments include:

There are several surgical approaches to treat megacolon, such as a colectomy[8] (removal of the entire colon) with ileorectal anastomosis (ligation of the remaining ileum and rectum segments), or a total proctocolectomy (removal of colon, sigmoid and rectum) followed by ileostomy or followed by ileoanal anastomosis.

See also

References

  1. ↑ "megacolon" at Dorland's Medical Dictionary
  2. 1 2 3 Megacolon, Chronic at eMedicine
  3. 1 2 Horton KM, Corl FM, Fishman EK (2000). "CT evaluation of the colon: inflammatory disease". Radiographics 20 (2): 399–418. doi:10.1148/radiographics.20.2.g00mc15399. PMID 10715339.
  4. ↑ Porter NH (1961). "Megacolon: a physiological study". Proc. R. Soc. Med. 54: 1043–7. PMC 1870487. PMID 14488085.
  5. ↑ Lim DK, Mahendran R (2002). "Risperidone and megacolon" (PDF). Singapore Med J 43 (10): 530–2. PMID 12587709.
  6. ↑ Hommes, DW; Sterringa, G; van Deventer, SJ; Tytgat, GN; Weel, J (May 2004). "The pathogenicity of cytomegalovirus in inflammatory bowel disease: a systematic review and evidence-based recommendations for future research.". Inflammatory bowel diseases 10 (3): 245–50. PMID 15290919.
  7. ↑ Koeberle F (1963). "Enteromegaly and cardiomegaly in Chagas disease". Gut 4 (4): 399–405. doi:10.1136/gut.4.4.399. PMC 1413478. PMID 14084752.
  8. ↑ Stabile G, Kamm MA, Hawley PR, Lennard-Jones JE (1991). "Colectomy for idiopathic megarectum and megacolon". Gut 32 (12): 1538–40. doi:10.1136/gut.32.12.1538. PMC 1379258. PMID 1773963.

External links

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